Switch panel R0

Christoph TackChristoph Tack wrote 10/06/2019 at 08:26 • 2 min read • Like

Revision 0 was all well and good, but  the big clock IO panel PCB is relatively costly and won't find any usage in other projects.  It serves mainly as a carrier for functionality that is already on modules (displays, light sensor).  The fifteen LED/switch combinations might be split up in four identical sections of four switches each.  There would be one module carrying only three switches.  It would add cost in wiring and connectors, but this switch module could easier find usage in other projects.  I would be able to use four of the five prototypes sent to me.  These switch modules would also fit the 100mm square template of the PCB manufacturer.  The different modules could then be mounted on a laser cut panel.  A separate module would be needed for the rotary encoder.  Buy them, not make.

Switch module

Keyboard scanning

The clock-io-panel uses matrix keyboard scanning.  It requires 8 IO lines for 15 switches.

It's only added here as a reference, because it's a clever circuit: If not enough IO lines had been available, there would be an alternative approach:

Using less IO less for keyboard scanning

This technique would require only 5 IO lines for 15 switches (max. 20 switches).  The downside is that 5 diodes need to be added.  This probably won't work with an SX1509 or similar which has a built in keypad scanning engine.